To fix the condition of the doors, sensitive elements are used in the form of electronic sensors. The most popular and in demand are the simplest samples called reed switches. As an element of the “smart home” system, a reed switch on the door is widely used to protect various household objects.
Description of reed sensors and operating principle
Known types of reed sensors on the door have a similar device and differ only in structural details. They are made in the form of a sealed glass flask, inside which there are two working contacts from permalloy. To increase the reliability of switching, the latter are processed with a thin coating based on noble metals. Outside pins are used to connect them to an electrical circuit. The inside of the flask is filled with an inert gas (or a vacuum is created in them), which allows to extend the life of the product and increase its ability to resist corrosion.
The principle of operation of the device is based on the mutual attraction of the contacts due to the approximation of an external magnetic field. In this case, the source of the latter's origin is not important: is it an electromagnet or a permanent magnet. Under its action, the contacts of the reed switch are magnetized and attracted, overcoming the elastic forces. They are in a closed state until the action of the field that triggered the operation ceases. After that, due to intrinsic elasticity, the contacts return to their previous (open) position.
Types of sensors and their characteristics
Like other contact products, according to their performance characteristics, reed switches are:
- switching, designed for two positions with one throwing contact plate;
- disconnecting, in the design of which a closed (in normal condition) contact is provided;
- make, having one open contact.
The reed switch on the door, triggered by opening the contacts, acts differently. When an external field appears, its plates are magnetized by one polarity and begin to repel. Switching type products have a middle contact of non-magnetic material, closed in the normal state. Under the action of a magnet, the open contacts close, and the non-magnetic plate remains in its original position.
According to the features of the inclusion and registration / notification of operation, door opening sensors are divided into the following types:
- bistable devices;
- wireless products;
- Wi-Fi sensors;
- sound devices.
The former have their own built-in magnet, which keeps the contacts in a switched state after removing the external field. The last three types differ only in the way they are included in the electric circuit (without using wires or with them) or the presence / absence of sound.
Design features
By design, the door opening sensors are divided into elements with dry switching contacts and mercury samples. The first - the simplest devices, characterized by the presence of "bounce". This term means spurious vibrations that occur when a circuit is opened and opened. If they are present, a single contact operation leads to a series of random switching, which disrupts the operation of electronic circuits.
The second variety is characterized by the fact that a drop of mercury is placed inside the sealed flask.It reliably wets the contacts, eliminating chatter and reducing their transient resistance.
The advantages of sensors include ease of installation and compactness, allowing you to mount the element in any convenient place. Their tightness is also noted, which is especially appreciated in rooms with high humidity. Among the disadvantages are low strength and low noise immunity.
Application and installation features
Reed type sensors are installed on moving or fixed parts of monitored objects (doors, in particular) that provide access to the room. They guarantee reliable operation of security equipment when trying to enter buildings. For the system to function properly, it will be necessary to supply electric power to it from the local wired line.
By installing an extensive network of reed switch sensors, it is possible to organize a reliable security system throughout the house, costing a minimum of costs. You can install these elements anywhere - on glass windows, on the doors of safes, as well as inside apartments on the front doors. The features of their installation include the mandatory placement on the internal surfaces of objects. In advanced models of sensors, their triggering is provided with simultaneous notification by mobile phone.
Popular manufacturers
Among the known models of reed sensors used to monitor the condition of the doors, the following samples stand out:
- wired magnetic devices used in security alarm systems such as PSM MC;
- sensors for opening doors and windows of the magnetic contact type COMK 1-3;
- wired magnetic contact device for doors / windows with alarm protection PST MC35;
- Wireless reed switch for opening doors (with support for broadcast frequency 433 MHz).
The “smart” reed switch SkyGuard RG-G31S belongs to the same series. This miniature but technologically advanced REDMOND device guarantees the impossibility of uncontrolled hacking and the safety of property located in the house. Sensors are used for remote monitoring of doors and windows at the following facilities:
- in apartments of urban buildings;
- in country cottages;
- in garages remote from the house or adjacent to it.
In addition, they are used to monitor the status of secret cabinets, secret drawers and safes.
The “smart” reed switch from the manufacturer REDMOND works synchronously with the Ready for Sky Guard mobile application. Upon detection of any movements in the apartment, accompanied by the opening of the doors, he immediately sends an alert to the smartphone.
